The present invention relates to casting of metals and alloys, and to casting vessels and methods.
The high costs of titanium associated with its extraction, melting, fabrication, and quality control have severely limited titanium use for applications other than the aerospace industry and niche corrosion resistance applications. Nearly 50% of the cost of titanium can be attributed to fabrication costs. Currently, most wrought titanium products are derived from massive cylindrical ingot which must be broken down by multiple steps of forging and rolling.
Continuous casting of steels has been practiced for many years and involves pouring a stream of steel melt into an open-bottomed, water-cooled, permanent mold. The molten steel is solidified as it travels the length of the mold and is concurrently drawn out of the open bottom of the mold directly to rolling mills. However, direct transfer of steel continuous casting technology to the titanium industry is complicated because molten titanium is such a reactive metal relative to ceramic materials typically used to fabricate the melt handling components of a continuous casting system.
There is a need for ceramic melt handling components that are compatible with molten titanium and its alloys as well as other reactive metals/alloys that may be amenable to continuous casting. Compatibility includes not only the reduction of chemical reactivity between the melt handling components and the molten reactive metal/alloy but also the mitigation of thermal shock sensitivity which arises from the combination of rapid thermal stress gradient formation during casting and the inherent brittleness of common ceramic materials.
An object of the present invention is to satisfy this need.
The present invention provides in one embodiment a one-piece, composite, open-bottom melt containment vessel, having a crucible section and an integral withdrawal or discharge section, that is fabricated in a manner from materials that exhibit compatibility with a molten reactive metal or alloy, such as, for example, titanium and its alloys. In a particular embodiment, a one-piece, composite continuous casting mold has an open-bottom crucible section to contain the molten metal or alloy and an integral open-bottom tubular withdrawal section. The integrated crucible and withdrawal sections comprise an inner thermal sprayed melt-contacting layer that is selected to be compatible with the molten metal or alloy and an outer thermal sprayed back-up layer, the layers being thermal sprayed in a manner to impart thermal shock resistance to the integrated crucible and withdrawal sections. An induction coil is positioned about the open bottom crucible section to melt and/or heat the metal or alloy therein, while the withdrawal section is not actively heated so that molten metal or alloy is solidified as it travels the length of the withdrawal section for withdrawal of a shaped continuous cast product (e.g. bar, rod, etc.) from a lower open end of the withdrawal section.
The present invention provides in another embodiment a one-piece, composite open bottom melt holding vessel having an open-bottom crucible section to contain molten metal or alloy to be atomized and an integral open-bottom tubular molten metal or alloy discharge section proximate a gas atomizing nozzle. The integrated crucible and discharge sections comprise an inner thermal sprayed melt-contacting layer described above compatible with the molten metal or alloy and an outer thermal sprayed back-up layer, the layers being thermal sprayed in a manner to impart thermal shock resistance to the integrated crucible and discharge sections. The discharge section is positioned relative to the atomizing nozzle such that molten metal or alloy discharged from the discharge section is atomized to form powder.
The aforementioned objects and advantages of the present invention will become more readily apparent from the following detailed description taken with the following drawings.